In the method of driving and ejecting ink by sound waves as disclosed in U.S. Pat. No. 4,751,529, ultrasonic waves produced by a piezoelectric transducer are transmitted from an ultrasonic wave buffer rod at a glass medium, and refracted from a spherical concave lens, and focused at the ink surface for ejecting individual droplets of ink. Another method as disclosed in U.S. Pat. No. 4,751,534 fills up the depression of the original concave lens by another medium while maintaining the refraction and focus functions as well as a smooth flow of the ink transport. In 1991, U.S. Pat. No. 5,041,849 disclosed a manufacturing technology that substitutes the aforementioned original concave lens by a multi-level Fresnel lens to simplify the manufacturing process, while maintaining the focusing function. In 2000, U.S. Pat. No. 6,045,208 disclosed a two-layer fraction and focus method, and a second ink layer can be focused at the ink surface more quickly, and an elongated stripe-pattern focusing lens is produced by using the cross-section of the Fresnel lens as the cross-section of stripe pattern ink, so that the focal points are connected with each other into a line, and ink droplets are in the form of a stripe pattern. U.S. Pat. No. 6,154,236 and European Patent Publication No. 0,683,405 disclosed an ink-jet head with a double-layer flow, and an upper layer of the ink-jet head provides for an ink flow, so that ultrasonic waves are focused at the surface of a nozzle disposed at the top of the upper layer, and the flow at a lower layer of the ink-jet head provides for dissipating heat, so that the heat produced by a piezoelectric transducer is carried away by the fluid. These technologies can be applied in a color filter coating process.
In view of the description above, the aforementioned patents utilize sound waves or ultrasonic waves and the Fresnel lens for the focusing, but the methods of driving and ejecting droplets of ink by focusing sound waves as disclosed by Elrod and Handimioglu have not been applied in color filter coating technology. European Patent Publication No. 0,683,405 simply applies a method of using the Fresnel lens to focus and eject ink in a color filter coating process, but such patented invention still emphasizes on the two-layer refraction and focus method or a printer device (as disclosed in U.S. Pat. No. 6,045,208) only. The ultrasonic ink-jet head as disclosed in the foregoing patents utilize the ultrasonic wave on only one side of the piezoelectric transducer, and the ultrasonic wave on the opposite side of the piezoelectric transducer penetrates through a backing layer and discharges into the air. Therefore, the highly efficient ink-jet head in accordance with the present invention features a higher efficiency of using sound energy than the aforementioned conventional ultrasonic ink-jet heads.
In view of the aforementioned shortcomings and deficiencies of the prior art, the inventors of the present invention based on years of experience in the related industry to conduct extensive researches and experiments and finally developed a highly-efficient ultrasonic ink-jet head and a fabrication method for the same in accordance with the present invention to overcome the shortcomings and deficiencies of the prior art.